Analyzing the molecular basis of enzyme stability in ethanol/water mixtures using molecular dynamics simulations

One of the drawbacks of nonaqueous enzymology is the fact that enzymes tend to be less stable in organic solvents than in water. There are, however, some enzymes that display very high stabilities in nonaqueous media. In order to take full advantage of the use of nonaqueous solvents in enzyme catalysis, it is essential to elucidate the molecular basis of enzyme stability in these media. Toward this end, we performed μs-long molecular dynamics simulations using two homologous proteases, pseudolysin, and thermolysin, which are known to have considerably different stabilities in solutions containing ethanol. The analysis of the simulations indicates that pseudolysin is more stable than thermolysin in ethanol/water mixtures and that the disulfide bridge between C30 and C58 is important for the stability of the former enzyme, which is consistent with previous experimental observations. Our results indicate that thermolysin has a higher tendency to interact with ethanol molecules (especially through van der Waals contacts) than pseudolysin, which can lead to the disruption of intraprotein hydrophobic interactions and ultimately result in protein unfolding. In the absence of the C30-C58 disulfide bridge, pseudolysin undergoes larger conformational changes, becoming more open and more permeable to ethanol molecules which accumulate in its interior and form hydrophobic interactions with the enzyme, destroying its structure. Our observations are not only in good agreement with several previous experimental findings on the stability of the enzymes studied in ethanol/water mixtures but also give an insight on the molecular determinants of this stability. Our findings may, therefore, be useful in the rational development of enzymes with increased stability in these media.     

A scenario for torus T destruction via a global bifurcation

We show a scenario of a two-frequency torus breakdown, in which a global bifurcation occurs due to the collision of a quasi-periodic torus T² with saddle points, creating a heteroclinic saddle connection. We analyze the geometry of this torus-saddle collision by showing the local dynamics and the invariant manifolds (global dynamics) of the saddle points. Moreover, we present detailed evidences of a heteroclinic saddle-focus orbit responsible for the type-II intermittency induced by this global bifurcation. We also characterize this transition to chaos by measuring the Lyapunov exponents and the scaling laws.     

Abundance of stable periodic behavior in a Red Grouse population model with delay: a consequence of homoclinicity

Shrimp-shaped periodic regions embedded in chaotic regions in two-dimensional parameter spaces are of specific interest for physical and biological systems. We provide the first observation of these shrimp-shaped stability regions in a parameter space of a continuous time-delayed population model, obtained by taking the delays as bifurcation parameters. The parameter space organization is governed by the presence of infinitely many periodicity hubs, which trigger the spiraling organization of these shrimp-shaped periodic regions around them. We provide evidence that this spiraling organization in the parameter space is a consequence of the existence of homoclinic orbits in the phase space.     

Ring fibre laser with interferometer based in long period grating for sensing applications

This work presents two distinct configurations based on phase-wavelength conversion using a ring fibre laser with two different long period gratings interferometer topologies. The sensors are interrogated by analysing the wavelength change of the emission laser, which is directly dependent on the interferometer phase change. The first configuration integrates a Mach-Zehnder interferometer, which is based on a pair of long period gratings and is used as sensing head for bending radius and longitudinal strain measurement. The second configuration, comprehends a Michelson interferometer, which is based on a single LPG and a fibre end mirror and is used as a liquid level sensor or as an optical refractometer.     

Mullite Based Compositions Prepared by Sol-Gel Techniques

Ceramic powders and gels in the multi-alumina system with different compositions were prepared by sol-gel method. The preparation of gels was done in strong acidic conditions and also with the addition of ammonia. The powders were prepared by dropping the sols on a hot plate. The effect of water/alkoxide and ethanol/alkoxide ratios was studied together with the type of catalyst used (hydrochloric acid or ammonia). The thermal evolution of materials was followed by thermal analysis, X-ray diffraction, specific surface area measurements and electron microscopy. The morphology of powders was also studied. The characteristic exothermic peak attributed to a good mixing degree of the Al and Si species was observed at ∼980°C. The intensity of this exothermic peak was more pronounced in gels than in sol-gel derived powders. The crystalline phases formed are related with the preparation conditions and with the thermal treatment. The crystallisation of mullite and transient phases of alumina were observed in powder samples heat treated at 1000°C while in gel samples mullite was the only crystalline phase detected.     

Cryptography with chaos at the physical level

In this work, we devise a chaos-based secret key cryptography scheme for digital communication where the encryption is realized at the physical level, that is, the encrypting transformations are applied to the wave signal instead to the symbolic sequence. The encryption process consists of transformations applied to a two-dimensional signal composed of the message carrying signal and an encrypting signal that has to be a chaotic one. The secret key, in this case, is related to the number of times the transformations are applied. Furthermore, we show that due to its chaotic nature, the encrypting signal is able to hide the statistics of the original signal.